Two-stroke engine with scavenging air blower



Dec. 1, 1953 A. SCHNURLE ETAL TWO-STROKE ENGINE WITH SCAVENGING AIR BLOWER Filed March 5. 1949 6 Sheets-Sheet 2 /nken/ons: 4 WWW W M Mr M M an;

Mfnesses:

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Dec. 1, 1953 A. SCHNURLE EI'AL ,660,98

TWO-STROKE ENGINE WITH SCAVENGING AIR BLOWER Filed March 3; 1949 6 Sheets-Sheet 5 M/nesses: 4 wrap/any:

4 6 W wMvaQmL $4 Dec. 1, 1953 A. SCHNURLE ETAL 2,660,939

TWO-STROKE ENGINE WITH SCAVENGING AIR BLOWER Filed March 5. 1949 6 Sheets-Sheet 4 bwen fora":

Mfneisfas': aw/* Dec. 1, 1953 'A. SCHNURLE ET AL TWO-STROKE ENGINE WITH SCAVENGING AIR BLOWER 6 Sheets-Sheet 5 Filed March 3, 1949 Ewen/om:

Dec. 1, 1953 A. SCHNURLE ETAL TWO-STROKE ENGINE WITH SCAVENGING AIR BLOWER Filed March 5, 1949 6 Sheets-Sheet 6 MM Ma a 4 01% aim fi Patented Dec. 1, 1953 IT'FED FSTTATES .i-mem {"OFFIZCE 'rwofs'rnonannema WITESGAYENGING 7 AIR BLGWER Adolf Schniirle, Johann Kopf, Otto Elwertf and Emil- Hiirz;- Stuttgart Germany; said :Kopf, said -Elw'ert, and said: iHiirz; assignors; to 1 said -Schniirle; -.Ger.trud Schniirle; sole heir; of-zsaid 1 .zgAdOlf: Schniirle, deceased Application March 3, 1949, Serial Noz'79g492 .Claims'priority, applieationfiermany Dc'toberlqi, 1948 HClaims. (Cl.123-*-55) v ,drive, is not. takenloirlthe impeller drive .pinion inventiona relates to V -type. twmstroke pygleaengineamith a-sgearrdriven turbo -b1ower chwith a scayenaingzzam receiver located .inside thezen inez crankcase-:betwe n-1th two cylinder thezamcunt-of -air aswiour cycle engines of -the same output. Ascentrifugalor. turbo. blower is gsparticularlysuitable-asscavenging,pumpior two- -zzcxcle enginessasitlnsztype fb10wer-can handle very large quantities of air at low pressure. "The soavenging pressurevshonldbe kept. as low ascompatibleuwithsan Badequate-scavenging; eiiect in ordento reduce theipower'required for driving. the

scavenging-gsystem, i. enthe abloweriits he receiver; the-massages tosthecylinders; and-the cylindempcrtslshouldbelsidesignedr toinsurez, the bestsrpossibleiaconditions-z for anzsundisturbed air flow. All passages should bezkept'shortand of sasufilciently: large-area; sand; as far as. bends are necessaryi toaalterr-the. direction; of :the air. now, they .shouldshave aalarge'radius of. :curvature.

Accordinglto thirinvention :theximpeller oi the blower isiarrangedizadjacentzto the front end; of the scavengingzainreceiver. I. ;."I he intake opening ofi:-.the'-:-;bloweriszia'cin'gz forward. .The impeller shaft is suppcrted on bearings zwithin-said'scavengingsair receiver.

in*order to keep :the overall length of the engine as=shortas possible the" crankshaft 'gear e v or the' impeller drive is 'locatedfwholly-or partially ii'i the"*planeof-the crank arm closest' to. the front main hearing of the *engine or: is. made integral with said crank armix' Ii the: distance 'i b'etween i-mpel'lei'shaft and'crankshaft is relative-i ly' large; thesimpellen drive gear train may also 1v contain am intermediate gear: between r the; imffi8118f shaft =piniorr'andithe crankshaft gear; 1 the ratio ofthe diameters" onthe crankshaitgear'and of the impelled shaft pinion -being':=proportiona1;

to the geari'eduction required in the-blower drive.

112- of advantage -to place the fuel injection pump ontop of the zscaven'ginglair :receiver:--beween -the two cylinder banks; -The'drive'o'f t the afton:-tiresflywheelsside of 4 the==enginer or, more advantageousl -ofhthe impeller shaftpthisalatter 1.1;

Itrcthdueia ihjectiommumps e hanks: llWQ:cycle.:engines,.-require.almost double blower'ei'omthe,samerinurpesez jail-parts of Y the 1 fuel indection' pump'may be taken-foil thecranke;

YZEEhB iuel injectionzzpump;

.. .but 'off somev other .pinion, also .mounted on"v the impeller shaft but; farther, towards the flywheel end of .said shaft; the flowconditions. oi..,.the

scavenging. air.- are greatly improved. as outlined later. in this specification.

Accordingto, anotherieature of the invention,

, the space provided as passage for. the scavenging air from the diffuser into the receiver, is preferably designed-as a disk-like. annular space-having. two openings; to the rear. portion. of the re- .ceiven Further-details as-.regards=the.,specia1 design of this passageare described in asubsequent part. of this specification.

;.In the accompanying: drawings Fig. 1 is a longitudinal .section throughwthe ,Fig. 2 is a cross section through the diifuser -shown. inFig. l.

j.- Fig. 3 is a lengitudinal section'of another v engine.

Figs..4 and5-are cross-sections oitwo different types of difiusers to be used; in engines ofthe design shown: in Fig. 3.

-.Fig 6; is a1rlonsitudinahsection.of.another v engine.

Fig. 7 is a modified; drixge gear train for thefuel injection pump-in-an engine otherwise-similar to that of Fig. 6.

The illustrated:.-engines; are 4; cylinder 90 V typetwo-cycle.engines witlr two engine cylinders .-:in-.each--.bank.e,;. Howevenathe invention is =-.not

limited tolenginesg ofthe. above type.- ,Thev angle may be smaller; or .largerthan 90-.and the. number of cylindersmaywbe,larger than 4.

; A i cylinder engine: oi.the above basicedesign is well suited tote-used; as agvehiclepower plant,

- as its 'overrall dimensions; are. relatively v.small.

The -crank- -throws-; of such an engineare, 180

.' apartaresulting in. a; firing order... of 4.- equally spaced pcweriimpulsesn A i;-cylindentwo..stroke cycle V: engine 1 of; this, type with;I equallyflspaced power impulses ,can be compared to.an-.8-. cyl=inder 4 two-stroke; -cycle1ineline; en ine as; far; as; speed '7 fluctuations: due: to. :itorque v,variatiens are. .con-

--cerned.

1 generate relatively largeforceiccupleswhich; cancounterweights.v ycle; inel-inexeneines afideenerate; couples .which In a e-cylindentwog cy cle in-line;- engine :with equally spaced powerlim-pulsesthe inertia-forces bejssiully unterhalanced by; .crankshaft cylinder and at-cylinder two- ;cannot:-be;:iullyzabalancedm lTheifcouples; of a 4- cylinder two-cycle V engine, however, can be fully counterbalanced by counterweights. A 6- cylinder two-cycle v engine with unequally spaced power impulses is inherently well balanced but has relatively large torque fluctuations, Whereas with equally spaced power impulses such a 6-cylinder engine will have a smooth torque but relatively large couples which cannot be fully counterbalanced by counterweights.

A l-cylinder two-cycle 90 V engine, therefore, is particularly suited to serve as a power plant for a vehicle. I) e to the relatively small speed fluctuations and the absence of unbalanced inertia forces and couples a centrifugal blower can be used as scavenging air supplier, as the operation of the blower at the required high speeds does not result in additional stresses on the blower drive gears due to unbalanced inertia forces and does not cause additional stresses on the impeller shaft bearings due to gyro action .of the impeller. .l urtherniore, a cylinders operating with equally spaced power impulses are sumcient to allow the use of a centrifugal blower as scavenging air supplier, as the scavenging periods of the l cylinders overlap to such a deree that the scavenging port area uncovered by the engine pistons remains practically constant. The scavenging air flow, thus, is practically free of fluctuations, so that a centrifugal air blower can well be utilized as scavenging air supplier.

A i-cylinder two-cycle 96 V engine, besides being fully balanced by counterweights for primary inertia forces and couples, is also balanced for secondary couples, so that no gyro moments can be generated in the impeller of the blower. The secondary inertia forces of a ll-cylinder engine of this type are compartively small. They act perpendicularly to the V angle center plane and occur close to the center of gravity of the engine. These secondary forces, therefore, only tend to move the crankshaft, andl hence the engine, in a lateral direction, the amount of this lateral movement being approximately 0.1 to 0.2 mm. The engine with the impeller shaft will consequently not be tilted by these secondary inertia forces, so that no moments will act on the impeller shaft bearings. The importance of mounting the impeller shaft parallel to the crankshaft is, therefore, apparent.

In addition, in diesel engines the flywheel is generally of comparatively large size, so that it acts itself as a gyroscopic stabilizer.

The curve of the scavenging air pressure, plotted against engine speed, shows that the engine cylinders are supplied the same quantity of scavenging air per revolution at all engine speeds. The scavenging pressure required to obtain a constant quantity of scavenging air for each scavenging period of the cylinders increases with the square of the engine speed. The pressure of the scavenging air furnished by a centrifugal blower also increases with the square of the engine speed. This is particularly important for vehicle engines operating within a wide range of speed.

The prejudice against using centrifugal blowers in two-stroke cycle engines operating at widely varying speeds for vehicles has been based on the erroneous premises that centrifugal blowers would not supply sufficient air pressure for scavenging and charging the engine cylinders. The opinion prevailed that only constant-displacement blowers would furnish air at the pressure required at low speed operation. The invention shows this prejudice to be unfounded.

In the engine shown in Figs. 1 and 2, numeral d l designates the engine cylinders of the left bank, 2 those of the right bank. The crankshaft 3 has two connecting rods mounted side by side on each crank pin. Accordingly, one of the cylinder banks is set off to the rear relative to the other bank, the distance of offset being equal to the axial width of one big-end bearing of the connectingrods. The flywheel l is attached to the rear end of the crankshaft 3. The scavenging air receiver 5 extends throughout the entire length of the crankcase between the bottom portions of the cylinders. The receiver is supplied with scavenging air by a centrifugal blower with an impeller 6 whose impeller shaft '5 has a driven pinion 8'. The impeller shaft is mounted 7 parallel to the crankshaft 3. The intake opening 9 of the impeller is facing forward. The impeller issurrounded by a diffuser with guide vanes. Air

is inducted through an intake pipe communicating with the intake opening 9 of the blower.

The impeller drive comprises a large spur gear I l fastened to the'cr'ank arm closest to the front main bearing. This crankshaft gear may be cushioned by springs inserted in slots cut into the crank arm as well as into the said gear (see Fig. 6). An intermediate gear 52 meshes with the crankshaft gear H and the pinion 3. 'The fact that the impeller drive is taken off the front crank arm reduces the overall length of the engine.

It can be seen in Fig. 1 that the scavenging air receiver 5 immediately joins the blower 6; the receiver extending to the wall it, is located to the rear of the impeller. The air delivered by the impeller, after passing through the diffuser,

is deflected towards the receivert by the outside wall M of the diffuser. The front portion of the receiver is here designed as a disk shaped annular chamber it.

In order to reduce the overall length of the engine the bearing support [6 of the impeller shaft is located within the receiver 5. This arrangement of the impeller shaft, however, makes the design of the connecting passages between the annular chamber l5 and the receiver 5 difiicult. According to the invention, apertures are provided on either side of thebearing support 86. In the design shown in Figs. 1 and 2 the apertures ll and it (see Fig. 2) are connected by the passage 49., The direction of air how in Fig. 2 as well as in subsequent drawings is indicated by arrows. Fig. 2 shows that the air after entering the receiver flows around the lower portions of the cylinders.

The receiver 5, which is arranged inside the crankcase between the two banks of cylinders, has lateral ducts connecting to the air passages of the cylinders. It is expedient to use the reverseloop scavenging method withair passages located on either side of theexhaust passages.

According to Fig. l the fuel injection pump 20 on top of the receiver is driven from the flywheel end of the engine by the gears 2i, 2?. and 23. The gear 2t drives the ,oil pump. The free'inertia forces of the reciprocating and rotating masses of the engine are balanced by acounterweight 25 attached to the front end of the'crankshaft in front of the diffuser; This counterweight cannot be fastened to the crank armclosest to the front main bearing of the engine'as this crank arm is a part of the blower drive. A further counterweight may be fastened, for instance, to'the flywheel 4. f

In the design shown in Figs. 3,.and4 the previously used numerals.'designate thesame respec- EBB W989 tive parts as in Figs. 1 and-'2. In order to dispense with a separate gear trairrfor driving the fuel injection pump 20 and to reduce the overall-length of the engine, the fuel injection -pump: is driven fro'mithe-impellershaft. As'shown in Fig. 3, a gear 26 of the-fuel-injectionpump meshes with the pinion '8'. Thegear trairr for d riving' the fuel injection pump thus passes through the receiver, so that the connection between-the receiver and the chamber I5 has to beeifected by separate apertures on either side of thetimpellerqbearing support and of the walls covering. the gears8- and 26...

In the blower design shownin Fig. .4. the;air leaning theldifiuser of thejblower enters into. two spiral shaped chambers 28 and 29." These chambers are located between the diffuser and the receiver and their large ends are connected to the receiver by openings 3!} and 3| respectively. All bends in the path of the air flow are designed with the view of keeping the deflection to the air and therefore the resistance to the air flow at a minimum.

In the modified blower design shown in Fig, 5 the air enters the spiral casing 32 after leaving the diffuser. The spiral chamber extends through an angle of 360 and its large end communicates with the receiver through the opening 33.

In the engine according to Figs. 3 and 4, the pertaining oil pump 34 is driven from the front end of the engine crankshaft. Hence, no increase in overall length of the engine is required on account of the oil pump drive.

In order to obtain good conditions of flow for the air passing from the annular chamber I5 into the receiver 5, guide vanes may be provided in the chamber I5 to deflect the air to the openings between the chamber I5 and the rear portion of the receiver.

In Fig. 6 the previously used numerals are again used for like parts. The drive of the blower is taken off the crank arm closest to the front main bearing. The crankshaft gear II of the blower drive is of the spring cushioned type. The drive of the fuel injection pump 23 is taken off a pinion 35 on the impeller shaft I. Pinion 35 has a smaller diameter than the impeller drive pinion 8 and meshes with a gear 36 on the shaft 31 of the fuel injection pump. Gear 36. in comparison with gear 26 in Fig. 3, is relatively small and the connecting openings between the diffuser and the receiver are accordingly larger.

In the engine shown in Fig. 6 the blower housing 38 is designed as a separate casing bolted to the crank case 39, whose front wall is plane and easy to machine straight. The front bearing of the impeller shaft I is supported in a separate support I3 inserted into the crankcase.

In order to accommodate large openings for the passage of the air from the blower to the receiver 5, the gear keyed to the drive shaft of the injection pump can be further reduced in diameter, if intermediate reduction gears are provided in the fuel injection pump drive between impeller and fuel pump shaft. Such a design is shown in Fig. 7. The gear train of the fuel injection pump drive consists of the gears 8, M, 42 and 43.

We claim:

1. In a two-cycle engine having a crankcase and a crankshaft with crank arms and having. two V- arranged banks of cylinders forming an angular through space between each other, in combination, a scavenging-air receiver extending along the bottom of said space and being integral with said crankcase, centrifugal scavenging-air blower 6 means dispos'edad jacent to said banks at the forwardend' of said crankcaseg said blowervmeans comprisinga housing and an impeller disposed in said housing and having a shaft parallel to said crankshaft at the height-of said receivei said housinghaving a rearward portion integral with said crankcase andhaving in said portion an an-- nular space--behind--said impeller and in direct communicationwi-th said receiver, a gear transmission connecting'said crankshaft with said impeller shaft and having a spur gear disposed on saidcrankshaft; said gear-being joined with'the most forward crankrarm' and. extending in the planeof said crank arm.

- 2. In'anengine according to claim 1, said 7 blower housing having an intake duct portion at the forward side of said crankcase, and mass balancing weight means mounted on said crankshaft outside of said crankcase and below said intake duct portion of said housing.

3. In a two-cycle engine having a crankcase and a crankshaft and having two V-arranged banks of cylinders forming an angular space between ea-ch other, in combination, a scavengingair receiver extending along the bottom of said angular space, a centrifugal scavenging-air blower mounted on said crankcase substantially at the height of said receiver and having a centrifugal impeller with an impeller shaft parallel to said crankshaft, a train of spur gears drivingly connecting said crankshaft with said impeller shaft and disposed in a radial crankshaft plane located on the receiver side of said impeller, said blower having an air intake conduit on its side away from said receiver and having an annular pressure space located between said impeller and said receiver, and passages connecting said pressure space with said receiver, said passages extending parallel to the crankshaft at the height of the receiver and passing through said plane on opposite sides respectively of said gear train.

4. In a two-cycle engine having a, crankcase and a crankshaft and having two V-arranged banks of cylinders forming an angular space between each other, in combination, a scave ing-air receiver extending along the bottom of said angular space, a centrifugal scavengingair blower mounted on said crankcase substantially at the height of said receiver and having a centrifugal impeller with an impeller shaft parallel to said crankshaft, a train of spur gears drivingly connecting said crankshaft with said impeller shaft and disposed in a radial crankshaft plane located on the receiver side of said impeller, said gear train having a spur gear on said crankshaft and a pinion on said impeller shaft and having an intermediate gear meshing with said spur gear and with said pinion, said intermediate gear having a smaller diameter than said spur gear, said blower having an air intake conduit on its side away from said receiver and having an annular pressure space located between said impeller and said receiver, and passage means connecting said' pressure space with said receiver and traversing said plane at the height of said receiver and on both respective sides of said pinion and intermediate gear.

5. In an engine according to claim 3, said crankshaft having crank arms, said plane of said gear train being coincident with the crank arm closest to said blower, and said gear train having'a spur gear joined with said latter crank arm.

ADOLF scHNfiRLE. JOHANN KOPF.

OTTO E13WERT.

EMIL HORZ. 10

References Cited in the file of this patent UNITED STATES PATENTS Name Date 15 Willoughby Feb. 3, 1903 Number Number Number Name Date Hoersting Mar. 12, 1918 Moss Apr. 18, 1922 Schneider Oct. 13, 1936 Boivie June 10, 1941 Straub Dec. 9, 1941 Szekely July 25, 1944 FOREIGN PATENTS Country Date France Aug. 25, 1913 France May 6, 1936 France June 15, 1942 Germany Aug. 27, 1924 Great Britain May 1, 1940 

